It was mentioned in a FancyZones thread a few months ago.
Thank you for pointing that out. I have to use Windows 10 often enough to wish for something like that, and had been looking, but FancyZones was the closest I'd found yet.
Related, bug.n is a DWM clone written in AutoHotkey, of all the things. I used it at work a few years ago, and I was very satisfied.
DisplayFusion is one I've used for years for splitting screens into virtual displays. Plus altering what elements show on the taskbar for those screens.